Electronic portal imaging devices (EPIDs) are important tools for treatment verification in Radiation Therapy. Most EPIDs developed so far for portal imaging application [using megavoltage (MV) x-rays] use a Cu plate/phosphor screen to absorb x-rays and convert their energies into light, and the light image is then read out by different ways depending on the design of a given EPID [see L. Boyer et al., “A review of electronic portal imaging devices (EPIDs),” Med. Phys. 19,1-16(1992)]. The main problem with this approach is that the Cu plate/phosphor screen must be thin (˜2 mm thick) in order to obtain a high spatial resolution, resulting in a low x-ray absorption or low quantum efficiency (QE), which is typically on the order of 2-4% as compared to the theoretical limit of 100%.
Therefore, it would be very advantageous to provide an x-ray detector with both the quantum efficiency and spatial resolution that can be used for portal imaging applications including megavoltage cone beam computed tomography (MVCT).